Active matrix substrate and producing method of the same

ABSTRACT

An active matrix is furnished with an insulating substrate; a plurality of scanning lines and signal lines provided on the insulating substrate in a matrix pattern; pixel electrodes provided in areas enclosed by the scanning lines and signal lines, respectively; switching elements electrically connected to the scanning lines, signal lines, and pixel electrodes, respectively; a resistance control element for electrically connecting two lines selected arbitrary from the scanning lines and signal lines while controlling its own resistance value in response to a voltage applied thereto. According to the above arrangement, it has become possible to increase a margin of the active matrix substrate for the static electricity and improve the production yield without increasing the number of the producing steps.

FIELD OF THE INVENTION

The present invention relates to an active matrix substrate havingformed thereon a matrix of non-linear elements serving as switchingelements, such as thin film transistors, and to a producing method ofthe same.

BACKGROUND OF THE INVENTION

In a general liquid crystal display element, a display pattern is formedon the screen by selectively driving a matrix of pixel electrodes. Inother words, in the above liquid crystal display element, when a voltageis applied across a selected pixel electrode and an opposing electrode,a liquid crystal interposed between these two electrodes as a displaymedium is optically modulated, and such an optical modulation isrecognized as a display pattern.

The active matrix driving method is known as a driving method of theabove pixel electrodes. In this method, a matrix of independent pixelelectrodes are connected to their respective switching elements, so thateach pixel electrode is driven by the ON/OFF action of the switchingelement. An example of the switching element is a non-linear element,such as a thin film transistor (hereinafter, referred to as TFT), an MIM(metal insulator metal) element, a MOS (metal oxide semiconductor)transistor element, and a diode.

As shown in FIG. 15 as an example, an active matrix substrate using TFTsas the switching elements is arranged in such a manner that a pluralityof parallel scanning lines 104 are provided to intersect at right angleswith a plurality of parallel signal lines 105.

A pixel electrode 102 is provided to each rectangular area enclosed bythe scanning lines 104 and signal lines 105. Also, a TFT 101 functioningas the switching element is provided in the vicinity of eachintersection of the scanning lines 104 and signal lines 105.

Each TFT 101 comprises a gate electrode 101 g connected to the scanningline 104 electrically, a source electrode 101 s connected to the signalline 105 electrically, and a drain electrode 101 d connected to thepixel electrode 102 electrically.

The switching element like the TFT 101 is produced by repeating the filmforming and etching steps of a conductor layer, a semiconductor layer,and an insulating layer. Thus, a static electricity is often generatedduring the producing process or transportation process from oneapparatus to another, the switching elements formed on the substrate aresusceptible to the static-induced damage.

To solve the above problem, various methods have been proposed toprotect the switching elements and the like from the static electricitygenerated during the producing process.

For example, a method disclosed in Japanese Laid-open Patent ApplicationNo. 106788/1988 (Tokukaisho No. 63-106788) is illustrated in FIG. 16, inwhich a conductor short-ring 108 is provided to interconnect all theinput terminals electrically. To be more specific, scanning line inputterminals 106 connected to the scanning lines 104 in an active matrixportion 103 and signal line input terminals 107 connected to the signallines 105 in the active matrix portion 103 are interconnectedelectrically through the conductor short-ring 108. According to thisarrangement, a static electricity inputted into any of the scanning lineinput terminals 106 and signal line input terminals 107 can be dispersedto all the other input terminals 106 and 107 through the conductorshort-ring 108.

In other words, when a static electricity is inputted one of thescanning line input terminals 106 and signal line input terminals 107,the input static electricity is dispersed to all the other inputterminals 106 and 107 through the conductor short-ring 108interconnecting these input terminals 106 and 107 electrically. Thus, ifa static electricity is inputted into one of the scanning line inputterminals 106, the switching elements 101 and pixel electrodes 102connected to the corresponding scanning line 104 are not affected by theinput static electricity.

However, if the input terminals are interconnected through the conductorshort-ring 108 as shown in FIG. 16, the conductor short-ring 108 must beremoved before a driver is mounted to each input terminal. Therefore,there is no static electricity preventing means in the steps after thedriver is mounted, and the switching elements and the like formed on thesubstrate may be damaged by the static electricity.

To solve the above problem, the above reference discloses an othermethod of preventing the switching elements and the like from the staticelectricity generated during the producing process, which is illustratedin FIG. 17. More specifically, the scanning lines 104 and signal lines105 between the active matrix portion 103 and the scanning line inputterminals 106/signal line input terminals 107 are interconnectedelectrically through a semiconductor short-ring 109 of high resistancemade of a semiconductor having a high resistance. According to thisarrangement, a static electricity inputted into any of the scanning lineinput terminals 106 and signal line input terminals 107 can be dispersedto all the other input terminals 106 and 107.

In other words, when a static electricity is inputted into any of thescanning line input terminals 106 and signal line input terminals 107,the input static electricity is dispersed to all the other inputterminals 106 and 107 by means of the semiconductor short-ring 109 ofhigh resistance through the scanning lines 104 and signal lines 105.

When all the lines are interconnected through the semiconductorshort-ring 109 of high resistance in the above manner, it is notnecessary to remove the semiconductor short-ring 109 of high resistancebefore the driver is mounted to each input terminal. Consequently, thestatic-induced damage to the switching elements is prevented in thesteps not only before but also after the driver is mounted.

However, when the active matrix substrate uses the above semiconductorshort-ring 109 of high resistance, it becomes quite difficult tostabilize a resistance value of the semiconductor layer during theproducing process, and a problem occurs if the resistance value of thesemiconductor short-ring 109 of high resistance is not set to anadequate value. That is, when the resistance value of the semiconductorshort-ring 109 of high resistance is too small, there occurs a seriousdefect, namely, leakage between the input terminals. On the other hand,when the resistance value of the semiconductor short-ring 109 of highresistance is too large, the semiconductor short-ring 109 of highresistance can not function as a short-ring.

Further, in the method of using the semiconductor layer as theshort-ring, if a channel etch type TFT is used as the switching elementof the active matrix portion 103, the semiconductor layer which will bemade into the short-ring must be masked by a photoresist when thesemiconductor layer is produced concurrently with the TFT.

Therefore, this method can not adopt a short-cut process, in which thegap in the TFT is etched using the source and drain electrodes as themask. In other words, since the photoresist is not used in the aboveshort-cut process, the photoresist is not left on the semiconductorlayer in the portion which will be made into the short-ring.Consequently, the semiconductor layer which is supposed to be made intothe short-ring is also etched away when the channel portion (gap) of theTFT is etched.

Therefore, as previously mentioned, to protect the unwanted etching ofthe semiconductor layer, an additional step is necessary to form aphotoresist on the semiconductor layer which will be made into theshort-ring before the gap of the TFT is etched. This not only increasesthe number of the steps in the producing process of the active matrixsubstrate, but also extends the producing time as well as increasing themanufacturing costs.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an activematrix substrate which can increase a margin for a static electricityand improve the production yield without increasing the number ofproducing steps, and a producing method of such an active matrixsubstrate.

To fulfill the above object, an active matrix substrate of the presentinvention is furnished with:

an insulating substrate;

a plurality of scanning lines and signal lines provided on theinsulating substrate in a matrix pattern;

pixel electrodes, each of which being provided to areas enclosed by thescanning lines an signal lines, respectively;

switching elements electrically connected to the scanning lines, signallines, and pixel electrodes, respectively; and

a resistance control element for electrically connecting at least twolines selected arbitrary from the scanning lines and signal lines, theresistance control element being capable of varying a resistance valuethereof under control in response to a voltage applied thereto.

The above active matrix substrate is furnished with the resistancecontrol element which electrically connects at least two lines selectedarbitrary from the scanning lines and signal lines and can vary aresistance value thereof under control in response to a voltage appliedthereto. Thus, it has become possible to stabilize a resistance betweenthe lines.

If the charges of an external static electricity enter into one of thescanning lines/signal lines connected to the resistance control element,the charges migrate to the other line through the resistance controlelement. Thus, when the resistance control element is provided betweenevery adjacent lines, the external charges entering into any of thelines can be dispersed to the other lines through the resistance controlelement in a satisfactory manner.

Consequently, it has become possible to eliminate the static-inducedbreakdown of the pixel electrodes and switching elements in the activematrix substrate caused by friction while the active matrix substrate istransported or moved, thereby making it possible to increase a margin ofthe active matrix substrate for the static electricity and improve theproduction yield.

Also, to fulfill the above object, a producing method of an activematrix substrate of the present invention is composed of the steps of:

forming a first conductive film used as a scanning line material on aninsulating substrate;

forming scanning lines, scanning electrodes, scanning electrodes of thinfilm transistors used as 2-terminal elements by patterning the firstconductive film into a predetermined shape;

forming a first insulating layer, a first semiconductor layer, and asecond insulating layer sequentially over an area including the scanninglines, scanning electrodes, and the scanning electrodes of the thin filmtransistors used as the 2-terminal elements;

forming a channel protecting layer by patterning the second insulatingfilm substantially in a same shape as the scanning electrodes and thescanning electrodes of the thin film transistors used as the 2-terminalelements;

forming a second semiconductor layer which will be made into a contactlayer over an area including the scanning lines, scanning electrodes,and the scanning electrodes of the thin film transistors used as the2-terminal elements;

forming channel portions of the thin film transistors and the contactlayer by patterning the first and second semiconductor layers into apredetermined shape, respectively;

forming a second conductive film which will be made into signal lines,signal electrodes, drain electrodes, signal electrodes, and drainelectrodes of the thin film transistors used as the 2-terminal elementsover an area including the contact layer;

forming the signal lines, signal electrodes, drain electrodes, and thesignal electrodes and drain electrodes of the thin film transistors usedas the 2-terminal elements by patterning the second conductive film intoa predetermined shape;

forming a third conductive film which will be made into pixelelectrodes; and

forming the pixel electrodes by patterning said third conductive filminto a predetermined shape.

According to the above producing method, the 2-terminal elements whichcontrol a resistance between the lines and the switching elements whichdrive the pixel electrodes can be produced concurrently. Therefore, boththe 2-terminal elements and switching elements can be composed of thechannel etch type thin film transistor. Thus, the producing process doesnot have to include a separate step to produce the 2-terminal elementsthat altogether constitute the short-ring for eliminating the staticelectricity from the switching elements. Consequently, the active matrixsubstrate having the short-ring can be produced in a shorter time.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of an active matrix substrate of thepresent invention;

FIG. 2(a) is a schematic plan view illustrating a section in thevicinity of a short-ring portion provided to the active matrix substrateof FIG. 1;

FIG. 2(b) is a cross section taken on line B—B of FIG. 2(a);

FIG. 2(c) is a cross section taken on line C—C of FIG. 2(a);

FIG. 3 is a graph showing a relation between a voltage and a currentacross the terminals connected through the short-ring portion;

FIG. 4(a) is a flowchart detailing a producing method of the entireactive matrix substrate of FIG. 1;

FIG. 4 (b) is a flowchart detailing a producing method of the section inthe vicinity of the short-ring portion of the active matrix substrate ofFIG. 1;

FIG. 5 is a schematic plan view showing a section in the vicinity of thepixel electrodes of the active matrix substrate of FIG. 1;

FIG. 6 is a cross section taken on line A—A of FIG. 5;

FIG. 7(a) is a schematic cross section of a section in the vicinity ofanother short-ring portion provided to the active matrix substrate;

FIG. 7(b) is a cross section taken on line D—D of FIG. 7(a);

FIG. 8 is a schematic plan view of an active matrix substrate having ashort-ring in a scanning line input terminal portion side alone;

FIG. 9 is a schematic plan view of an active matrix substrate having theshort-ring in a signal line input terminal portion side alone;

FIG. 10(a) is a schematic plan view showing a section in the vicinity ofa further short-ring portion provided to the active matrix substrate;

FIG. 10 (b) is a cross section taken on line E—E of FIG. 10(a);

FIG. 11(a) is a flowchart detailing a producing method of the entireactive matrix substrate of FIG. 10 (a)

FIG. 11(b) is a flowchart detailing a producing method of the section inthe vicinity of the short-ring portion of the active matrix substrate ofFIG. 10(a);

FIG. 12(a) is a schematic plan view showing a section in the vicinity ofstill another short-ring portion provided to the active matrixsubstrate;

FIG. 12(b) is a cross section taken on line F—F of FIG. 12(a);

FIG. 13(a) is a flowchart detailing a producing method of the entireactive matrix substrate of FIG. 12(a);

FIG. 13(b) is a flowchart detailing a producing method of the section inthe vicinity of the short-ring portion of the active matrix substrate ofFIG. 12(a);

FIG. 14 is a schematic plan view showing a section in the vicinity ofstill another short-ring portion provided to the active matrixsubstrate;

FIG. 15 is a schematic plan view showing a section in the vicinity of aconventional active matrix substrate;

FIG. 16 is a schematic plan view showing a conventional active matrixsubstrate; and

FIG. 17 is a schematic plan view showing another conventional activematrix substrate.

DESCRIPTION OF THE EMBODIMENTS

The following description will describe an example embodiment of thepresent invention by way of a liquid crystal display device (activematrix type liquid crystal display device) using an active matrixsubstrate of the present invention.

As shown in FIG. 6, an active matrix type liquid crystal display devicein accordance with the present invention comprises an active matrixsubstrate 21, an opposing substrate 22, and a liquid crystal 23 sealedin a space between the above two opposing substrates 21 and 22.

The active matrix substrate 21 includes a transparent insulating glasssubstrate 1 having formed thereon pixel electrodes 2 and switchingelements 3 connected to each other electrically.

A gate electrode 3 g of each switching element 3, a gate insulating film4, a semiconductor layer 5, a contact layer 6, an etching stopper 43serving as a channel protecting layer, the pixel electrodes 2, and adrain electrode 3 d and a source electrode 3 s of each switching element3 are sequentially formed on the insulating glass substrate 1 frombottom to top in the drawing.

The opposing substrate 22 includes a transparent insulating glasssubstrate 1 having sequentially formed thereon a photo-blocking film 7,a color filter 8, and an opposing electrode 9 from top to bottom in thedrawing.

As shown in FIG. 5, a set of gate lines 10 serving as the scanning linesand a set of source lines 11 serving as the signal lines are provided onthe active matrix substrate 21 in such a manner to intersect at rightangles with each other. One pixel electrode 2 is provided to each areaenclosed by the gate lines 10 and source lines 11.

Further, a Cs line 12 serving as an additional capacity of each pixelelectrode 2 is provided below the pixel electrode 2 along the gate lines10 and orthogonal to the source lines 11.

Each line used herein is made of a photo-blocking conductive film, suchas a tantalum film and an aluminium film.

The active matrix substrate 21 will be described in detail in thefollowing.

As shown in FIG. 1, the active matrix substrate 21 includes an activematrix portion 31, a scanning line input terminal portion 32, and asignal line input terminal portion 33.

The active matrix portion 31 includes a matrix of the pixel electrodes2, the switching elements 3 electrically connected to the pixelelectrodes 2 individually, a plurality of the parallel gate lines 10,and a plurality of the source lines 11 aligned to intersect at rightangles with the gate lines 10. In FIG. 1, the Cs lines 12 serving as theadditional capacities of the pixel electrodes 2 are omitted for theexplanation's convenience.

The scanning line input terminal portion 32 comprises a plurality ofscanning line input terminals 34, to which the gate lines 10 areconnected electrically through gate connecting lines 36, respectively.Although it is not shown in the drawing, a driving circuit is connectedto each scanning line input terminal 34.

The signal line input terminal portion 33 comprises a plurality ofsignal line input terminals 35, to which the source lines 11 areconnected electrically through source connecting lines 37, respectively.Although it is not shown in the drawing, a driving circuit is connectedto each signal line input terminal 35.

Further, a short-ring 38 is provided to the gate connecting lines 36 andsource connecting lines 37 which are formed between the active matrixportion 31 and the scanning line and signal line input terminal portions32 and 33, respectively. The short-ring 38 is provided to electricallyinterconnect, namely, short-circuit, all the gate lines 10 and sourcelines 11.

The short-ring 38 comprises a plurality of 2-terminal elements(resistance control elements) 39 composed of the TFTs, which is arrangedin such a manner that a pair of the 2-terminal elements connected in aninverted position in parallel are placed between every two adjacentlines, thereby short-circuiting all the lines when a predeterminedvoltage is applied to the 2-terminal element.

For further understanding, the 2-terminal element 39 will be explainedin the following. Here, the 2-terminal element 39 connected to the gatelines 10 side is explained as an example, and since the 2-terminalelement 39 connected to the source lines 11 side is of the samestructure, an explanation of which is omitted herein.

As shown in FIG. 2(a), a pair of the 2-terminal elements 39 are providedto each gate connecting line 36 to electrically interconnect the gatelines 10 and the scanning line input terminals 34. As shown in FIGS.2(b) and 2(c), both the gate connecting lines 36 and scanning line inputterminals 34 are made out of a same metal layer 41, and atop of which anITO (indium tin oxide) film 42 is layered.

In other words, as shown in FIG. 2(b), the 2-terminal element 39 iscomposed of the TFT comprising a gate electrode 39 g formed as anintegral part of the metal layer 41, and atop of which the gateinsulating film 4, semiconductor layer 5, and a drain electrode 39 d anda source electrode 39 s formed over a contact layer 6 are sequentiallylayered from bottom to top in the drawing.

The etching stopper 43 serving as a channel protecting layer is formedat a gap portion 39 a of the 2-terminal element 39.

As shown in FIG. 2(a), the drain electrode 39 d of one 2-terminalelement 39 is connected electrically to the source electrode 39 s ofanother 2-terminal element 39 provided to either of the adjacent gateconnecting lines 36, while the source electrode 39 s of the firstlymentioned 2-terminal element 39 is connected electrically to the drainelectrode 39 d of another 2-terminal element 39 provided to the otheradjacent gate connecting line 36.

The pair of the 2-terminal elements 39 provided to the same gateconnecting line 36 are connected in parallel and in such a manner thatthe source electrode 39 s and drain electrode 39 d of each 2-terminalelement 39 are placed in an inverted position. In short, signals flow inopposite directions through the pair of the 2-terminal elements 39provided to the same gate connecting line 36.

FIG. 3 shows a graph of the I-V characteristics when a voltage isapplied across two adjacent scanning line input terminals 34 eachprovided with the 2-terminal elements 39.

The graph reveals that when the voltage applied across the terminals ischanged in a range between −40V and 40V, the current across the samevaries smoothly in a range between −50 μA and 50 μA. This indicates thatthe 2-terminal elements 39 function as the short-ring even when a verylow voltage is applied. Therefore, the 2-terminal elements 39 canfunction as the short-ring in response to a weak static electricityclose to a point where the electrical breakdown of the semiconductoroccurs.

According to the above arrangement, each 2-terminal element 39 iscontrolled to change its own resistance value, that is, the readiness ofa current flow, in response to an applied voltage. Thus, it has becomepossible to stabilize a resistance value between the lines. This isbecause the resistance value between the lines, namely, the resistancevalue of the short-ring 38, is controlled using an ON resistance of theTFTs which are used as the 2-terminal elements 39. Therefore, the2-terminal elements 39 do not cause the leakage between the inputterminals that used to occur when the resistance value is too small, andcan function as the short-ring even when the resistance value is toolarge.

The 2-terminal element 39 of the present embodiment is arranged to havea resistance value of approximately 2 MΩ when a voltage of 25V isapplied across the scanning line input terminals 34. This arrangement ismade on the assumption that the 2-terminal elements 39 would be used inthe active matrix substrate whose gate lines 10 has a voltage of Vgh=15Vand Vgl=10V.

In other words, when the largest potential difference between thevoltages applied across the adjacent bus lines is 25V, the resistancevalue between the terminals is set in such a manner that the signals ofthe applied voltages Vgh and Vgl do not affect each other.

At the same time, the resistance value between the terminals must be setin such a manner that the unillustrated driver connected to eachscanning line input terminal 34 does not effect an excessive currentprotecting operation when the power source is turned on.

A producing method of the above-arranged active matrix substrate 21 willbe explained in the following with reference to FIGS. 4(a) and 4(b).FIG. 4(a) is a flowchart detailing a producing method of the entireactive matrix substrate 21, and FIG. 4(b) is a flowchart detailing aproducing method of a section in the vicinity of the short-ring portionof the active matrix substrate 21.

To begin with, the gate lines, gate electrodes, scanning and signalinput terminals are made out of a scanning line material (hereinafter,referred to as gate material) formed as a first conductive film in theentire active matrix substrate (S1). To be more specific, thetransparent insulating glass substrate 1 is coated with a 3000 Å-thickTa film, namely the scanning line material, through the sputtering.Then, the Ta film is patterned through the photolithography and etchedaway, whereby the gate lines 10, gate electrodes 3 g serving as thescanning electrodes of the switching elements 3, the gate connectinglines 36 extended from the gate lines 10, scanning line input terminals34, and signal line input terminals 35 are formed.

As shown in FIG. 4(b), first electrodes of the 2-terminal elements areformed in the section in the vicinity of the short-ring portionconcurrently with Si (S1′). To be more specific, the gate electrodes 39g are formed as the first electrodes of the 2-terminal elements 39 whichaltogether constitute the short-ring 38 by modifying the forming patternof the gate connecting lines 36 partially.

Here, in S1 and S1′, the etching of the Ta film can be carried out byeither the dry etching method which uses a plasma of a mixed gas ofCF₄O₂, or wet etching method which uses an etching liquid, namely, amixed liquid of hydrofluoric acid and nitric acid.

However, in case of the wet etching method, a Ta₂O₅ film having athickness ranging from 1000 Å to 10000 Å must be formed between theinsulating glass substrate 1 and Ta film to prevent the unwanted etchingof the insulating glass substrate 1. This means that the number of thesteps is greater in the wet etching method than in the dry etchingmethod. For this reason, the dry etching method is adopted as the methodof etching the Ta film herein.

In addition, although Ta (tantalum) is used as the gate material herein,Al (aluminium) and Mo (molybdenum) or an alloy of these elements arealso applicable.

Then, a gate insulating film (first insulating layer) which will be usedas the gate insulating film 4, and a semiconductor layer (firstsemiconductor layer) which will be used as the semiconductor layer 5,and an etching stopper film (second insulating layer) which will be usedas the etching stopper (ES) layer 43 are formed on the gate materiallayered over the insulating glass substrate 1 (S2). More specifically, a3000 Å-thick SiNx film, a 300 Å-thick a-Si(i) film, and a 2000 Å-thickSiNx film are formed sequentially in this order on the gate materiallayered on the insulating glass substrate 1 through the plasma CVDmethod as the gate insulating film 4, semiconductor layer 5, and etchingstopper layer 43, respectively.

Concurrently with S2, a gate insulating film to be used as the gateinsulating film 4 out of which the 2-terminal elements 39 thataltogether constitute the short-ring 38 will be made, a semiconductorlayer which will be used as the semiconductor layer 5, and an etchingstopper film which will be used as the etching stopper (ES) layer 43 areformed in the section in the vicinity of the short-ring portion (S2′).

Subsequently, the etching stopper layer 43 is patterned in both theentire active matrix substrate and the section in the vicinity of theshort-ring portion (S3 and S3′).

To be more specific, in S3 and S3′, an area which will be made into thepixel electrodes 2 and an area which will be made into the 2-terminalelements 39 that altogether constitute the short-ring 38 are patternedthrough the photolithography, and only the SiNx film on the top isetched away with a BHF liquid (hydrofluoric acid and ammonium fluoride)to leave the etching stopper layer 43 alone.

Alternatively, a 3000 Å-thick Ta₂O₅ film may be formed by anodizing thesurface of the gate lines 10 and the surface of the gate electrodes 3 gof the switching elements 3 before the gate insulating film 4 is formedby the plasma CVD method to ensure the insulation.

Then, an n+ layer (second semiconductor layer) which will be used as thecontact layer 6 is formed over the semiconductor layer which will beused as the semiconductor layer 5 in both the entire active matrixsubstrate and the section in the vicinity of the short-ring portion (S4and S4′). More specifically, a 400 Å-thick a-Si(n+) film or μc-Si(n+)film is formed over the semiconductor layer 5 as the n+ layer throughthe plasma CVD method.

Then, the semiconductor layer and n+ layer are patterned in both theentire active matrix substrate and the section in the vicinity of theshort-ring portion (S5 and S5′). More specifically, the a-Si(n+) film orμc-Si(n+) film and the a-Si(i) film are patterned into an insular shapeconcurrently through the photolithography and etching, whereby thecontact layer 6 is made out of the a-Si(n+) film or μc-Si(n+) layer andthe semiconductor layer 5 is made out of the a-Si(i) film.

Then, the gate insulating film (SiNx film) is patterned at a portioncorresponding to the terminal portion of the driver ICs and bus lines inthe entire active matrix substrate 21 (S6). Concurrently with S6, theinsulating film (SiNx film) over the first electrode connecting portionwhich will be made into the gate electrodes 39 g of the 2-terminalelements 39 is patterned in the section in the vicinity of theshort-ring portion (S6′).

Then, the SiNx film is etched away, whereby contact holes are made asconnecting portions through which the driver ICs and bus lines areconnected to each other. In case that the Ta₂O₅ film is formed beforethe gate insulating film 4 is formed, the Ta₂O₅ is etched away with theSiNx film.

Then, the source lines 11, and source electrodes 3 s and drainelectrodes 3 d of the switching elements 3 are made out of a sourcematerial (second conductive film) in the entire active matrix substrate(S7).

Concurrently with S7, the connecting lines, first electrodes, and secondelectrodes are formed in the section in the vicinity of the short-ringportion (S7′). More specifically, the gate connecting lines 36 andsource connecting lines 37, source electrodes 39 s, and drain electrodes39 d are formed as the connecting lines, first electrodes, and secondelectrodes, respectively.

In other words, in S7 and S7′, the insulating glass substrate 1 iscoated entirely with a 3000 Å-thick metal thin film made of Ti used asthe source material through the sputtering. Then, the metal thin film ispatterned through the photolithography and etched away, whereby thesource electrodes 3 s and drain electrodes 3 d of the switching elements3, source lines 11, the source electrodes 39 s and drain electrodes 39 dof the 2-terminal elements 39 that altogether constitute the short-ring38 are formed.

Although Ti is used for the metal thin film herein, Mo, Al, or an Alalloy can be used as well.

Then, the pixel electrodes 2 are made out of a third conductive film inthe entire active matrix substrate (S8). More specifically, a 1500Å-thick ITO film is formed through the sputtering as the thirdconductive film, and out of which the pixel electrodes 2 are formedthrough the subsequent photolithography and etching. The ITO film may bepatterned to be left on the source lines 11, so that the active matrixsubstrate 21 has a redundant structure for preventing the line breakingof the source lines 11.

Concurrently with S8, an ITO film is formed over the metal layer 41which will be made into the scanning line input terminals 34, and theITO film 42 is formed through the subsequent photolithography andetching (S8′).

The source electrodes 39 s and drain electrodes 39 d of the TFTs used asthe 2-terminal elements 39 that altogether constitute the short-ring 38are made out of the source metal film herein. However, as shown in FIGS.7(a) and 7(b), the 2-terminal element 39 can be replaced with a2-terminal element 49 made out of the conductive film out of which thepixel electrodes are also made, which will be described in thefollowing.

Each 2-terminal element 49 comprises a gate electrode 49 g formed as anintegral part of the metal layer 41, and a source electrode 49 s and adrain electrode 49 d made out of the conductive ITO film 42.

Alternatively, the source electrode and drain electrode of the2-terminal element may be made out of both the source metal film andconductive film to give the redundancy to the short-ring 38.

Finally, a 3000 Å-thick SiNx film serving as the protecting film isformed through the plasma CVD method to cover the entire portion wherethe electrodes are formed on the insulating glass substrate 1. Then, theSiNx film is patterned through the photolithography, and etched awaywith the BHF liquid (hydrofluoric acid+ammonium fluoride), whereby theSiNx film on the pixel electrodes 2 is removed and the active matrixsubstrate 21 is produced.

Then, an orientation film made of, for example, polyimide, is applied onthe surface of the active matrix substrate 21 where the pixel electrodes2 are formed through the printing method. Subsequently, the sameorientation treatment is applied to the opposing substrate 22 having thecolor filter 8 of FIG. 6 in the same manner. Then, the active matrixsubstrate 21 and opposing substrate 22 are laminated to each otherthrough an unillustrated sealing material, and the liquid crystal 23 isfilled in the space between the above two substrates 21 and 22, wherebythe active matrix type liquid crystal display device is assembled.

In the active matrix substrate 21 produced in the above manner, a pairof the 2-terminal elements 39 composed of TFTs are connected in aninverted position in parallel and placed in every two adjacent gateconnecting lines 36 and source connecting lines 37 as shown in FIG. 1.

Therefore, if an external static electricity enters into any of theinput terminals, the entering charges open the gates of the 2-terminalelements 39 that altogether form the short-ring 38, and are dispersed tothe adjacent input terminals to the following input terminalssequentially.

Consequently, compared with an active matrix substrate having noshort-ring 38, the frequency of the occurrence of the electricalbreakdown and characteristics displacement of the TFTs caused by thestatic electricity can be reduced significantly.

Thus, according to the active matrix substrate of the present invention,the short-ring does not have to be removed before the driver ICs areconnected like in the case where the semiconductor layer is used as theshort-ring. Thus, the adverse effect of the static electricity can beeliminated in the steps not only before but also after the driver ICsare mounted to the active matrix substrate.

In addition, since the resistance of the short-ring is controlled usingthe ON resistance of the TFTs, the resistance of the short-ring can bestabilized.

Moreover, according to the above active matrix substrate, the higher theapplied potential to each input terminal, the lower the resistance valueof the short-ring. Therefore, compared with the semiconductor short-ringconnected in series, a greater amount of charges can be dispersed.

Further, the above active matrix substrate is arranged in such a mannerthat the signals flow through a pair of the 2-terminal elements 39connected to the same connecting line in an inverted position inparallel and constituting the short-ring 38. Thus, the 2-terminalelements 39 can serve as the short-ring even when an amount of thecharges is very small.

The 2-terminal elements may be connected in series in alternatingdirections. However, in this case, the resistance of the resultingshort-ring becomes too large to efficiently disperse the staticelectricity to each input terminal in response to the charges below thebreakdown voltage of the 2-terminal elements.

In the present embodiment, the short-ring 38 is formed between theactive matrix portion 31 and the scanning line and signal line inputterminal portions 32 and 33 as shown in FIG. 1. However, the position ofthe short-ring 38 can be modified as shown in FIG. 8, for example. Thatis, the short-ring 38 may be formed between the active matrix portion 31and scanning line input terminal portion 32 alone. Likewise, as shown inFIG. 9, the short-ring 38 may be formed between the active matrixportion 31 and the signal line input terminal portion 33 alone.

As shown in FIGS. 2(b) and 7(b), each of the 2-terminal elements 39 thataltogether constitute the short-ring 38 is composed of the TFT havingthe etching stopper layer 43 to prevent the unwanted etching of thechannel portion of the semiconductor layer 5 herein. However, achannel-etch type TFT having no etching stopper layer 43 can be used asthe 2-terminal element as well.

In the following, an active matrix substrate using the channel-etch typeTFTs as the 2-terminal elements that altogether constitute theshort-ring 38 will be explained.

An example channel-etch type TFT is shown in FIG. 10(b) as a 2-terminalelement 61, which comprises a gate electrode 61 g formed as an integralpart of the metal layer 41, the gate insulating film 4, thesemiconductor layer 5, and a source electrode 61 s and a drain electrode61 d formed over the contact layer 6.

In the 2-terminal element 61, the semiconductor layer 5 and contactlayer 6 are etched away concurrently inside a gap portion 61 a.

Here, a producing method of the active matrix substrate using the2-terminal elements 61 will be explained with reference to FIGS. 10(a)and 10(b) and FIGS. 11(a) and 11(b). FIG. 11(a) is a flowchart detailinga producing method of the entire active matrix substrate, and FIG. 11(b)is a flowchart detailing a producing method of a section in the vicinityof the short-ring portion of the active matrix substrate.

To begin with, the gate lines, gate electrodes, scanning and signalinput terminals are made out of a gate material (first conductive film)in the entire active matrix substrate (S11). To be more specific, likeS1 of FIG. 4(a), the gate lines 10, gate electrodes 3 g serving as thescanning electrodes of the switching elements 3, gate connecting lines36 extended from the gate lines 10, and scanning line input terminalportion 32 and signal line input terminal portion 33 are formed.

Concurrently with S11, the first electrodes of the 2-terminal elementsare formed in the section in the vicinity of the short-ring portion(S11′). To be more specific, like S1′ of FIG. 4(b), the gate electrodes61 serving as the first electrodes of the 2-terminal elements 61 thataltogether form the short-ring 38 are formed.

Then, a gate insulating film (first insulating film), a semiconductorlayer (first semiconductor layer), and an n+ layer (second semiconductorlayer) are formed on the gate material layered on the insulating glasssubstrate 1, which will be used as the gate insulating film 4,semiconductor layer 5, and contact layer 6, respectively (S12) Morespecifically, a 3000 Å-thick SiNx film, a 300 Å-thick a-S1 (i) film, anda 400 Å-thick a-Si(n+) film or μc-Si(n+) film are formed on the gatematerial layered on the insulating glass substrate 1 through the plasmaCVD method as the gate insulating film 4, semiconductor layer 5, andcontact layer 6, respectively.

Concurrently with S12, an insulating film, a semiconductor layer, and ann+ layer are formed in the section in the vicinity of the short-ringportion, which will be used as the gate insulating film 4, semiconductorlayer 5, and contact layer 6, respectively (S12′).

Subsequently, the semiconductor layer and n+ layer are patterned in boththe entire active matrix substrate and the section in the vicinity ofthe short-ring portion (S13 and S13′). More specifically, in S13 andS13′, an area which will be made into the pixel electrodes 2 and an areawhich will be made into the 2-terminal elements 61 that altogetherconstitute the short-ring 38 are patterned through the photolithography,and the a-Si(i) film which will be used as the semiconductor layer 5,and the n+ layer made of the a-Si(n+) film or μc-Si(n+) film arepatterned into an insular shape concurrently through the dry etchingmethod.

Then, a gap portion of the n+ layer is patterned in both the entireactive matrix substrate and the section in the vicinity of theshort-ring portion (S14 and S14′).

In other words, in S14 and S14′, both the a-Si(i) film which will beused as the semiconductor layer 5 and the n+ layer made of the a-Si(n+)film or μc-Si(n+) film which will be used as the contact layer 6patterned into the insular shape in S13 and S13′ are separated into thesource electrode 3 s side and drain electrode 3 d side in each switchingelement 3, and into the source electrode 61 s side and drain electrode61 d side in each 2-terminal element 61 through the photolithography toform the channel portion in each of the switching elements 3 and2-terminal elements 61, respectively. The dry etching method using a(SF₆+HCl)-based gas is adopted for the above separating action. Here, agap portion 61 a in each 2-terminal element 61 is etched in such amanner to leave the a-Si(i) film of 500 Å-thick, so that the same willbe used as the semiconductor layer 5.

Subsequently, like S6 of FIG. 4(a), the insulating film (SiNx film) ispatterned at a portion corresponding to the driver ICs in the entireactive matrix substrate (S15). Then, the SiNx film is etched away,whereby contact holes are made as connecting portions through which thedriver ICs and the bus lines are connected to each other.

Concurrently with S15 and like S6′ of FIG. 4(b), the insulating film(SiNx film) over the first electrode connecting portions which will bemade into the gate electrodes 61 g of the 2-terminal elements 61 ispatterned in the section in the vicinity of the short-ring portion(S15′). Subsequently, the SiNx film is etched away, whereby the contactholes are made as connecting portions through which the driver ICs andbus lines are connected to each other.

Then, the source lines 11, and source electrodes 3 s and drainelectrodes 3 d of the switching elements 3 are made out of a sourcematerial (second conductive film) in the entire active matrix substrate(S16).

Concurrently with S16, the connecting lines, first electrodes, andsecond electrodes are formed in the section in the vicinity of theshort-ring portion (S16′). To be more specific, the gate connectinglines 36 and source connecting lines 37 are formed as the connectinglines, and in addition to the drain electrodes 61 d, the gate electrodes61 g and source electrodes 61 s are formed as the first and secondelectrodes of the 2-terminal elements 61, respectively.

Subsequently, the pixel electrodes 2 are made out of a third conductivefilm in the entire active matrix substrate (S17). To be more specific, a1500 Å-thick ITO film is formed through the sputtering as the thirdconductive film, and out of which the pixel electrodes 2 are formedthrough the subsequent photolithography and etching.

Concurrently with S17, an ITO film is formed on the metal layer 41 whichwill be made into the scanning line input terminals 34, and an ITO film42 is formed through the subsequent photolithography and etching (S17′).

Then, the active matrix substrate using the channel-etch type TFTs bothin the active matrix portion 31 and short-ring 38 is produced in theabove manner.

According to the above producing method, the channel portions are madein the switching elements 3 connected to their respective pixelelectrodes 2 and the 2-terminal elements 61 that altogether constitutethe short-ring 38 by etching the semiconductor layer 5 and contact layer6 concurrently. Thus, it has become possible to adopt the short-timeprocess, in which the source conductive film or pixel conductive film isused as the photo-mask when the channel portions are etched.

As shown in FIG. 12(b), an active matrix substrate produced through theabove short-cut process uses 2-terminal elements 71 that altogetherconstitute the short-ring 38, and each of which comprises a gateelectrode 71 g formed as an integral part of the metal layer 41, thegate insulating film 4, the semiconductor layer 5, and a sourceelectrode 71 s and a drain electrode 71 d formed over the contract layer6.

In each 2-terminal element 71, the semiconductor layer 5 and contactlayer 6 are etched concurrently inside gap portions 71 a using thesource electrodes 71 s and drain electrodes 71 d of the 2-terminalelements 71 as the mask.

Here, a producing method of the active matrix substrate using the2-terminal elements 71 will be explained with reference to FIGS. 12(a)and 12(b) and FIGS. 13(a) and 13(b). FIG. 13(a) is a flowchart detailinga producing method of the entire active matrix substrate, and FIG. 13(b)is a flowchart detailing a producing method of the section in thevicinity of the short-ring portion.

To begin with, the gate lines, gate electrodes, gate and source inputterminals are formed out of a gate material (first conductive film) inthe entire active matrix substrate (S21). Like S11 of FIG. 11(a), thegate lines 10, gate electrodes 3 g serving as the scanning electrodes ofthe switching elements 3, gate connecting lines 36 extended from thegate lines 10, and scanning line input terminal portion 32 and signalline input terminal portion 33 are formed.

Concurrently with S21, the first electrodes of the 2-terminal elements71 are formed in the section in the vicinity of the short-ring portion(S21′). Like S11′ of FIG. 11 (b), the gate electrodes 72 g serving asthe first electrodes of the 2-terminal elements 71 that altogetherconstitute the short-ring 38 are formed.

Then, a gate insulating film (first insulating film), a semiconductorlayer (first semiconductor layer), and an n+ layer (second semiconductorlayer) are formed on the gate material layered on the insulating glasssubstrate 1, which will be used as the gate insulating film 4,semiconductor layer 5, and contact layer 6, respectively (S22). Morespecifically, a 3000 Å-thick SiNx film, a 300 Å-thick a-Si(i) film, anda 400 Å-thick a-Si(n+) film or μc-Si(n+) film are formed on the gatematerial layered on the insulating glass substrate 1 through the plasmaCVD method as the gate insulating film 4, semiconductor layer 5, andcontact layer 6, respectively.

Concurrently with S22, an insulating film, a semiconductor layer, and ann+ layer are formed in the section in the vicinity of the short-ringportion, which will be used as the gate insulating film 4, semiconductorlayer 5, contact layer 6, respectively (S22′).

Subsequently, the semiconductor layer and n+ layer are patterned in boththe entire active matrix substrate and the section in the vicinity ofthe short-ring portion (S23 and S23′). More specifically, in S23 andS23′, an area which will be made into the pixel electrodes 2 and an areawhich will be made into the 2-terminal elements 71 that altogetherconstitute the short-ring 38 are patterned through the photolithography,and the a-Si(i) film which will be used as the semiconductor layer 5,and n+ layer made of the a-Si(n+) film or μc-Si(n+) film are patternedinto an insular shape concurrently through the dry etching method.

Then, like S16 of FIG. 11(a), the insulating film (SiNx film) ispatterned at a portion corresponding to the driver ICs in the entireactive matrix substrate (S24). Then, the SiNx film is etched away,whereby contact holes are made as connecting portions through which thedriver ICs and the bus lines are connected to each other.

Concurrently with S24 and like S16′ of FIG. 11(b), the insulating film(SiNx film) over the first electrode connecting portions which will bemade into the gate electrodes 61 g of the 2-terminal elements 71 ispatterned (S24′). Then, the SiNx film is etched away, whereby thecontact holes are made as connecting portions through which the driverICs and bus lines are connected to each other.

Then, the source lines 11, and source electrodes 3 s and drainelectrodes 3 d of the switching elements 3 are made out of a sourcematerial (second conductive film) in the entire active matrix substrate(S25).

Concurrently with S25, the connecting lines, first electrodes, andsecond electrodes are formed in the section in the vicinity of theshort-ring portion (S25′). To be more specific, the gate connectinglines 36 and source connecting lines 37 are formed as the connectinglines, and in addition to the drain electrodes 71 d, the gate electrodes71 g and source electrodes 71 s are formed as the first and secondelectrodes of the 2-terminal elements 71, respectively.

At this point, gap portions are patterned into the n+ layer in both theentire active matrix substrate and the section in the vicinity of theshort-ring portion. More specifically, gap portions 3 a of the switchingelements 3 in the active matrix portion 31 and gap portions 71 a of the2-terminal elements 71 that altogether constitute the short-ring 38 arepatterned.

In other words, in each switching element, the gap portion 3 a forming achannel region is formed by etching the semiconductor layer 5 andcontact layer 6 using the source electrode 3 s and drain electrode 3 das the mask. On the other hand, in each 2-terminal element 71, the gapportion 71 a forming a channel region is formed by etching thesemiconductor layer 5 and contact layer 6 using the source electrode 71s and drain electrode 71 d as the mask.

Subsequently, the pixel electrodes 2 are formed out of a thirdconductive film in the active matrix portion 31 (S26). To be morespecific, a 1500 Å-thick ITO film is formed through the sputtering asthe third conductive film, and out of which the pixel electrodes 2 areformed through the subsequent photolithography and etching. concurrentlywith S26, the ITO film is formed on the metal layer 41 which will bemade into the scanning line input terminals 34 in the section in thevicinity of the short-ring portion, and an ITO film 42 is formed throughthe subsequent photolithography and etching (S26′).

Then, the active matrix substrate using the channel-etch type TFTs bothin the active matrix portion and short-ring is produced in the abovemanner.

As previously mentioned (with reference to the graph of FIG. 3), theresistance value of the short-ring 38 formed in the active matrixsubstrate must be set in such a manner that the current value across theinput terminals varies smoothly with an applied voltage, so that a verysmall voltage can cause a current to flow across the terminals.

In the active matrix substrate produced in the above producing method,however, a satisfactory short-ring resistance may not be obtainedbecause of a defect of the 2-terminal elements that altogetherconstitute the short-ring. For example, if the photolithography isincomplete in the producing procedure, the resulting 2-terminal elementmay short-circuit. In this case, the line (scanning electrode or signalelectrode) connected to the short-circuited 2-terminal element isrecognized as a line defect (defect caused by the leakage between thelines) on the active matrix substrate.

However, since the short-ring is provided to prevent the staticelectricity inputted sporadically from the external and can be omittedafter the driver is mounted, the short-ring connected to the linerecognized as the line defect can be cut to eliminate the leakage,whereby the line defect on the active matrix substrate is eliminated.

Therefore, as shown in FIG. 14 as an example, the connecting portion ofa drain electrode 81 d of one 2-terminal element 81 and a sourceelectrode 81 s of the adjacent 2-terminal element 81 is reduced in widthto form a rectangular restriction portion 82 in the short-ring 38.According to this arrangement, the defect of the 2-terminal element 81,such as the short-circuit, can be readily eliminated with a laser cutteror the like in the steps after the driver is mounted.

In the present embodiment, the short-ring 38 is provided between theactive matrix portion 31 and the scanning line and signal line inputterminals 32 and 33. However, besides the above arrangement, theshort-ring 38 may be formed at the edge portion of the bus lines, orinside the active matrix portion 31 other than the display area but ifthe numerical aperture does not have to be concerned much, theshort-ring 38 can be formed in the display portion of the active matrixportion 31.

As has been explained, according to the above-explained active matrixsubstrate of the present embodiment, the resistance value between theinput terminals can be stabilized by providing the short-ring comprisingthe 2-terminal elements each having a controllable resistance value tothe input terminals. Consequently, it has become possible to increase amargin of the active matrix substrate for the static electricity,thereby improving the production yield of the liquid crystal displaydevices or the like using the above active matrix substrate of thepresent invention.

In the active matrix substrate of the present invention, the resistanceof the short-ring is controlled using the ON resistance of the TFTs,namely, the 2-terminal elements that altogether constitute theshort-ring. Thus, the resistance value of the short-ring can bestabilized in a more reliable manner.

In addition, the resistance value of the short-ring of the presentinvention drops as the applied potential rises, and therefore, theshort-ring of the present invention has better charge dispersing abilitycompared with the short-ring made of a semiconductor using a simpleserial resistance. Moreover, the short-ring of the present invention iscomposed of at least a pair of 2-terminal elements connected in paralleland having the conductive characteristics in the opposite directions.

Thus, the charges can be dispersed efficiently in response to even avery weak static electricity close to a point the where the electricalbreakdown occurs. Consequently, the active matrix substrate of thepresent invention can attain the effect that the charges of the staticelectricity can be dispersed efficiently in response to a wide range ofvoltages.

Further, according to the producing method of the active matrixsubstrate of the present invention, since the 2-terminal elements thataltogether constitute the short-ring are of the same structure as theTFTs serving as the switching elements in the active matrix portion.Thus, it has become possible to adopt the short-cut process, in whichthe channel-etch type TFTs are used as the switching elements of theactive matrix substrate, and most characteristically, the gap portionsare etched using the source and drain electrodes of the switchingelements as the mask.

Therefore, if both the switching elements and 2-terminal elements arecomposed of the channel etch type TFTs, the short-ring can be formedwithout adding an additional producing step, such as the patterning stepusing the photoresist.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. An active matrix substrate comprising: aninsulating substrate; a plurality of scanning lines and signal linesprovided on said insulating substrate in a matrix pattern; pixelelectrodes, each of which being provided to areas enclosed by saidscanning lines and signal lines, respectively; switching elementselectrically connected to said scanning lines, signal lines, and pixelelectrodes, respectively; and a resistance control element electricallyconnecting at least two lines selected arbitrarily from each of saidscanning lines and signal lines, said resistance control element varyinga resistance value between the at least two lines in response to avoltage applied to the resistance control element, the resistancecontrol element having two thin film transistors (TFTs), and an ONresistance of the TFTs controls the resistance value between the atleast two lines, wherein said each of said two thin film transistorseach have a source electrode of a first TFT electrically connected toand a drain electrode of the other TFT.
 2. The active matrix substrateof claim 1, wherein said two thin film transistors are channel-etch typetransistors.
 3. An active matrix substrate comprising: an insulatingsubstrate; a plurality of scanning lines and signal lines provided onsaid insulating substrate in a matrix pattern; pixel electrodes, each ofwhich being provided to areas enclosed by said scanning lines and signallines, respectively; switching elements electrically connected to saidscanning lines, signal lines, and pixel electrodes, respectively; and aresistance control element electrically connecting at least two linesselected arbitrarily from each of said scanning lines and signal lines,said resistance control element varying a resistance value between theat least two lines in response to a voltage applied to the resistancecontrol element, the resistance control element having two thin filmtransistors (TFTs), and an ON resistance of the TFTs controls theresistance value between the at least two lines, wherein said signallines and pixel electrodes are made of a same conductive film.
 4. Anactive matrix substrate comprising: an insulating substrate; a pluralityof scanning lines and signal lines provided on said insulating substratein a matrix pattern; pixel electrodes arranged in an array in saidmatrix pattern; switching elements electrically connected to saidscanning lines, signal lines, and pixel electrodes; and a first set oftwo parallel thin film transistors (TFTs) electrically connecting atleast one pair of said scanning lines or at least one pair of saidsignal lines, a second set of two parallel TFTs electrically connectingat least one of said scanning lines to at least one of said signallines, and said first set of TFTs smoothly varying a resistance valuebetween the at least one pair of said scanning lines or at least onepair of said signal lines in response to a voltage applied across thefirst set of TFTs wherein an ON resistance of the second set of TFTscontrols the resistance value between the at least one pair of saidscanning lines or at least one pair of said signal lines, said secondset of TFTs smoothly varying a resistance value between the at least oneof said scanning lines and at least one of said signal lines in responseto a voltage applied across the second set of TFTs, wherein an ONresistance of the second set of TFTs controls the resistance valuebetween the at least one of said scanning lines and at least one of saidsignal lines.
 5. An active matrix substrate comprising: an insulatingsubstrate; a plurality of scanning lines a n d signal lines provided onsaid insulating substrate in a matrix pattern; pixel electrodes, each ofwhich being provided to areas enclosed by said scanning lines and signallines, respectively; switching elements electrically connected to saidscanning lines, signal lines, and pixel electrodes, respectively; and aresistance control element electrically connecting at least two lines ofsaid scanning lines or at least two lines of said signal lines, saidresistance control element varying a resistance value between the atleast two lines in response to a voltage applied to the resistancecontrol element, the resistance control element having two thin filmtransistors (TFTs) each connected to both of said at least two lines,and an ON resistance of the TFTs controls the resistance value betweenthe at least two lines, wherein said TFTs include a first set of TFTssmoothly varying a resistance value between one pair of said scanninglines or one pair of said signal lines in response to a voltage appliedacross the first set of TFTs wherein an ON resistance of the second setof TFTs controls the resistance value between the one pair of saidscanning lines or at least one pair of said signal line, and a secondset of TFTs smoothly varying a resistance value between one of saidscanning lines and one of said signal lines in response to a voltageapplied across the second set of TFTs, wherein an ON resistance of thesecond set of TFTs controls the resistance value between the one of saidscanning lines and one of said signal lines.
 6. The active matrixsubstrate of claim 5, wherein said at least two lines connected throughsaid resistance control element are selected from said scanning lines.7. The active matrix substrate of claim 5, wherein said at least twolines connected through said resistance control element are selectedfrom said signal lines.
 8. A liquid crystal display device using theactive matrix substrate of claim 5.